1. Field of the Invention
This invention relates to power supplies, and more particularly relates to implementing redundant power supplies for increased efficiency at low power output.
2. Description of the Related Art
A power supply, sometimes known as a power supply unit or PSU, is a device or system that supplies electrical or other types of energy to an output load or group of loads. A power supply, in some embodiments may be configured to convert power in one form to another form, such as converting AC power to DC power. The regulation of power supplies is typically done by incorporating circuitry to tightly control the output voltage or current of the power supply to a specific value. The specific value is closely maintained despite variations in the load presented to the power supply's output, or any reasonable voltage variation at the power supply's input.
For example, in an electrical device such as a computer, the power supply is typically designed to convert an AC voltage input such as is traditionally provided by a conventional wall socket, into several low-voltage DC power outputs for transmission to the internal components of the computer. Conversion is sometimes performed in stages that may include different power supply topologies such as a rectification stage, a boost stage, buck stage, or other topology.
In some cases, two or more power supplies may be operated in parallel to provide redundancy for fault protection and to provide power beyond the full load capacity of a single power supply. In a redundant power system with two power supplies, each power supply typically operates most efficiently when operated near their full load capacity. However, if both power supplies are sharing the load and the load is at full load, each power supply provides only 50%, which is less efficient than a single power supply operating at 100%. Typically, load conditions require a total power output wherein each power supply provides less than 50% of its full load capacity. This is even more problematic because each power supply is operating at less than 50% where efficiency degrades rapidly. The situation is even worse if there are more than two power supplies in parallel.
Conventional art addresses this problem by completely shutting down one of two redundant power supplies when only one power supply is needed or when using two power supplies in parallel is more inefficient than operating a single power supply. However, a problem with this solution is that by completely shutting down one of the redundant power supplies, the power supply that is shut down is typically unable to recover quickly enough in the event of a failure of the other power supply to prevent a momentary power failure in a system receiving power from the power supplies. For example, if the power supplies are providing power to a computer system, and one of the power supplies fails while the other is shut down, the computer system may experience errors or a complete failure before the redundant power supply is able to restart and begin providing power to the computer system.
In some embodiments, capacitors may be provided with the power supplies to continue to momentarily output power in the event of a failure or power interruption. However, if the capacitors are too small, there may not be a long enough hold-up time for a backup power supply to start up and begin providing power. Conversely, if the capacitors are too large, then too much time may be required to charge up the capacitors of a power supply being started up prior to providing power to a load before the voltage regulated by the power supplies sags to an unacceptable level.
Thus, there is a need for a redundant power supply system that allows the power supplies to operate at maximum efficiency while still providing quick redundancy fault recovery in the event of a failure of one of the power supplies.